In a known manner, an electrochemical power source (a so-called “electrochemical battery”) comprises an electrochemical stack, constituted by at least two electrodes, made of a metal material for example, with different electronegative potentials, and in which a suitable electrolytic fluid is made to circulate.
This electrolytic fluid undergoes an increase in temperature when it is inside the electrochemical stack, due to the exothermicity of the chemical reactions that take place inside the same electrochemical stack.
As a rule, the electrolytic fluid has to be extracted from the electrochemical stack and cooled by suitable cooling systems, to avoid unsustainable heat drift in the system, and then put back into the electrochemical stack again.
Control of the temperature of the electrolytic fluid introduced into the electrochemical battery is an important parameter for correct operation of the power source, especially in those batteries where performance is affected by following factors:                leakage currents, i.e. leak electric currents that circulate inside the battery between the electrodes, which become electrically connected by the electrolytic fluid; and        internal resistance (also defined as series resistance) of the electrochemical stack.        
Both of these factors are affected by the temperature of the electrolytic fluid; in particular, as the temperature rises, the electric resistance of the electrolytic fluid drops and leakage currents rise, while the series resistance inside the stack drops.
Theoretical and experimental research has also revealed that the optimal working temperature depends on the power supplied by the electrochemical battery.
In particular, when low power is requested (i.e. the component linked to series resistance is low), the temperature of the electrolytic fluid can be advantageously reduced to limit internal leakage currents, which are more penalising for the system in these conditions.
Vice versa, when high power is requested, the temperature can be advantageously raised to reduce the series resistance of the electrochemical stack.
To enable adjustment of the temperature of the electrochemical fluid, it has been proposed to use a control system that comprises a heat exchanger, two tanks designed to contain electrolytic fluid and a thermostatic valve.
In particular, hot electrolytic fluid is taken from the electrochemical stack and transferred to a first tank, while a second tank contains cold electrolytic fluid, obtained by cooling hot electrolytic fluid that is made to flow through the heat exchanger.
The thermostatic valve has a first and a second inlet, respectively connected to the first and the second tank, an outlet connected to a fluid inlet of the electrochemical stack, and control means that can be operated to control the mixing of hot electrolytic fluid and cold electrolytic fluid to be fed to the electrochemical stack, to adjust the temperature of the mixed electrolytic fluid.
However, until now, no entirely satisfactory control systems exist for adjusting the temperature of the electrolytic fluid that is reintroduced into the electrochemical stack.
In particular, inside underwater vehicles, such as torpedoes, this temperature is generally set to a fixed, predetermined value.